1. Field of the Invention
The present invention relates to a method and apparatus for irradiating an object with temporally stable light, and more particularly, to a method and apparatus for irradiating simulated solar radiation, which needs to be irradiated in large light quantity and over a large area, in temporally stable light quantity and spectrum. The present invention also relates to a method and apparatus for irradiating a semiconductor device which is an object temporally responding relatively quickly to a temporal variation in light quantity over a sensitive wavelength range with temporally stable light.
2. Related Background Art
As a method for irradiating a semiconductor device with simulated solar radiation, Japanese Patent Application Laid-Open No. S61-269801 discloses a method of lighting and irradiation using a xenon lamp as a light source, using an expensive air mass filter for adjusting a spectral distribution and using an expensive stabilized DC power supply as a power supply source. Though this method is costly, it can secure temporal stability of light quantity relatively easily and is appropriate for a case where an object to be irradiated is small and the total price falls within an allowable range. However, the price of this method increases at an accelerating pace as the required irradiation area grows. This is because attempting to irradiate the entire surface of an object with substantially uniform light in response to an increase of the area of the object requires increases in size of components such as the air mass filter and other optical systems, which increases the degree of difficulty of manufacturing in an accelerating pace and further requires an increase in the capacity of the expensive stabilized DC power supply for the lamp, which is costly from the very beginning.
As one of methods for realizing a large area, Japanese Patent Application Laid-Open No. H11-26785 discloses a method for lighting a lamp using pulses. This method is effective in terms of reducing the capacity of a power supply for the lamp. However, the necessity for large size components such as an air mass filter and other optical systems remains the same and this method is still costly. Moreover, while this method takes into account the temporal stability of light quantity during a pulse lighting-up time, it ignores the temporal stability of continuous light quantity including a non-lighting-up time.